This invention involves a method and its associated building support structures for the modification and improvement of building construction, in particular for the modification of the construction of buildings with respect to resistance to strong winds and earthquakes in earthquake prone regions.
This invention is especially directed to, although not exclusively directed to, residential and office buildings that are composed of and are built using standardized structural elements and units that as wall units, floor units and roof units, that are constructed of lightweight material as well as of heavy weight material.
For buildings that are located in areas in which "high wind(s)" occur, designed herein as wind speeds of 130 to 350 miles per hour("mph"), it is essential that the building be constructed so that it is capable of resisting such wind speeds without being damaged or destroyed. It should be noted that wind speeds of 130 to 350 mph occur in hurricanes, thunderstorms and tornadoes. Accordingly, structures in any location subjected to such weather, including North and South America, South Asia, the Far East, Australia and Western Europe, need to be designed to withstand high winds.
Accordingly, in the earthquake prone regions building structures should be resistant against powerful earthquakes regardless what material they are built of. But as evidences show, collected from the earthquakes happened in the past throughout the world, where building structures are constructed of a various materials(lightweight, heavyweight or materials having a various degree of a strength), no building structures have displayed capability to withstand forces induced by earthquakes without being subjected to a severe damage or destruction.
A structure's ability to withstand high wind is primarily related to its weight, which is referred herein as the "natural gravity" of the structure. Accordingly, lightweight materials, such as wood, used in construction of dwelling houses and offices, are most vulnerable to damage caused by high wind since generally have relatively small resistance to high wind, everything else being equal. In fact, many structures constructed in the United States are made of wood and other lightweight materials and therefore are vulnerable to high wind. When such lightweight structures are subjected to high wind, their weight becomes extremely small and easy moveable by the horizontal force.
The term "relative gravity" of a structure as used herein refers to the additional force of weight of the structure generated by mechanically applying pre-stressing forces in the direction of the force of the structure's natural gravity. However, the "relative gravity" force does not affect the soil or other matter beneath the structure by adding forces on the soil; it is accumulated and distributed entirely within the structure itself.
Based on a large scale study that has examined the effects of high wind conditions having speeds of 130, 170, 200, 250, 300 and 350 mph on one, two and three-story structures, when such structures used as a dwelling house or an office structure are subjected to high wind, the structural consequences are as follows:
1. The gravity resultant of the structure is displaced from its natural position in direct proportion to the intensity of the wind speed. This causes severe disturbances in the structure's ability to withstand stress and is most evident in the walls of the structure.
2. High winds can change speeds suddenly. Walls of known structures have low, almost negligible transverse (flexural) stiffness as well as low, almost negligible inertial mass. When subjected to high wind such wall undergo vibrations. Walls that undergo vibrations develop additional load and transfer such additional load to the system of connectors and fasteners. In addition, structural units are composed of structural elements which are classified as primary, secondary and tertiary. It is said that secondary and tertiary elements are subjected to vibrations from multiple sources. As a result, the structure undergoes chaotic vibrations.
3. As a result of the above effects of high winds on the structure, the structure collapses.
Actual experience has verified the conclusion of such study in that the structure would indeed collapse under high wind conditions. In particular, hurricane Andrew which had wind speed of 164 mph and gust wind speeds of 198 mph on Aug. 24, 1992 when it struck South Florida, hurricane Opal which struck in 1995, and many other hurricanes and tornadoes had sufficient wind speeds to cause great damage to structures along their paths. In the earthquake prone regions existing wood structures may have better rating, means the wood structures ability to withstand seismic load is greater than its ability to resist high wind attacks, because seismic load induced on the structure by earthquake is function of gravitational mass and inertial mass of the structure. Meanwhile developed vibration inside structural units produces significant additional load on the system of anemic connectors and fasteners throughout the wood structure. These are reasons the collapses in the structures are along joint lines of the structural units: in the roof structure, wall structure, joint lines of wall units-roof units, joint lines of wall units-floor units.
Effects of an earthquakes in terms of a developing loads on the building structures constructed by heavyweight classical materials, such as brick, stone, reinforced concrete, steel, etc. are of much greater degree in comparison with wood structures due to much greater gravitational mass of those materials. Despite high strength of those materials, every earthquake of a greater intensity in the past have produced catastrophic damages to the buildings. A fresh example is Northridge earthquake which five years ago made huge damages to about 100 toll buildings in the Los Angeles area built of steel and reinforced concrete.
This invention is designed to address and solve the above problem caused when structures made of lightweight materials are subjected to high winds and earthquakes in the earthquake prone regions.
This invention is also designed to help in certain degree to solve the problem caused when structures built of heavyweight materials such as brick, stone, concrete block, reinforced concrete, steel, etc. are subjected to seismic load in the earthquake prone regions.